1. Field of the Invention
This invention relates to belt apparatus useful for rotating or turning an object and particularly to the field of tongs employing such a belt apparatus, both manually operated and power-driven tongs, of the type commonly used for making up and breaking apart threaded connections between tubular members and the like, and to processes for using such a belt apparatus or such a tong.
2. Description of the Prior Art
Jaw and Die Tongs
Present day tongs that are employed for coupling and decoupling threaded pipe sections are typically subject to one or more of a number of practical problems. Some examples are found in systems for the engagement and disengagement of sections of a casing or pipe string that is to be lowered into or removed from a well bore. Extremely high torques may have to be applied, due to combinations of factors such as the presence of corrosion, the existence of distortion, and pipe size and weight. High shock forces arise, both in the "make" direction of rotation when a shoulder is suddenly encountered, and in the "break" direction at initial engagement of the tong and disengagement of the threads. Moreover, the forces and pressures involved are at such levels that operation is seldom smooth and uniform. For example, with a power-driven tong, in excess of 50,000 foot-pounds of torque may be exerted, while relatively small die elements engage the pipe with extremely high force loadings. Consequently, it is common for slippage to occur, for the pipe surfaces to become marred or otherwise damaged.
Tubular members must be successively joined and lowered into the well or, conversely, separated and removed therefrom. Joint sections generally are circular, and the tubulars have no provision for keyed type engagement with a tong mechanism.
Grip elements, such as jaws with dies, can be provided with multiple serrations, or penetration features, to provide the interference contact needed at the joint surface. The progressive refinement of tubular materials and installation procedures and use practices has mandated limitation and control of grip element penetrations into the joint surfce. Consequently, the distribution and balance of grip element energizing forces are critical factors in the design, development and evaluation of such tong mechanisms.
Various mechanisms involving linkages, levers, wedges, and cams are in current use for the disposition and balance of the force components. Usually, grip elements, or dies, are arcuately disposed within carrier bodies, or jaws, which span a circumferential segment of the joint surface. A degree of compromise must be established to accommodate acceptable ranges of joint and mechanism dimensional tolerance.
Design compromises, common to the art, structure jaws to operate with very high load variations between leading and trailing dies, or resort to jaw guiding slides, or linkages, to control die contact and force delivery. However, all jaw guides absorb energy and detract from torque delivery. Also, extremely uneven die loading causes excessive marring or damage to the tubular surface.
The examples of prior art constructions mentioned also are susceptible to one or more of a variety of other problems. For example, fragments and dirt can enter into the cam devices that are typically used to urge the jaws or dies into engagement with the pipe, damaging the cams and causing the dies to lock in or out of position or dirt deposited in serrations in dies can inhibit proper die action, prevent proper penetration into the tubular to be rotated, and result in deleterious scarring of pipe.
Many designs also are such that die loading becomes increasingly asymmetrical as pipe size is reduced, substantially increasing die wear and the probability of damage. A power tong should preferably be able to cover a range of pipe sizes without difficulty, and if a further pipe size change is needed it should be effected with only an interchange of parts. Maintenance and life problems have an economic significance far in excess of the cost of the dies or even the pipe involved, because the down time that results when replacements or repair must be made involves not only material costs but also drilling rig and crew costs and the continuing charges for other specialized tools and equipment present at the drilling rig. Thus a power tong system which requires frequent replacement of dies or other elements or which causes undue damage to sections in a pipe string would be far inferior to a power tong system which operates steadily and uniformly.
The extremely high stresses and abrupt shocks encountered in a tong operation are usually attended by visible strains on the equipment and by vibrations and sharp impacts which results in a very short fatigue life for the parts involved and the unit as a whole. These are caused by overload or unbalanced force conditions which are further evidenced by undue wear, slippage or equipment damage.
Some tongs use drag or braking techniques to secure proper biting of the dies relative to the pipe. As the rotary is driven the head or other member supporting the dies is frictionally restrained to insure that the dies do not simply rotate with the rotary. In many power tong systems, a substantial part of the available energy is effectively used only for overcoming braking friction.
Belt and Chain Tongs
Instead of using jaws or dies to grip pipe, many tongs use an endless belt, chain or flexible material loop. Such tongs are disclosed in U.S. Pat. Nos. 3,799,010; 3,906,820; 3,892,140; 4,079,640; 4,099,479; and 4,212,212. Many problems are encountered with the use of such tongs.
(1) The length of an endless chain must be changed to accommodate tubulars of different size or means must be provided to maintain tubulars on a centered position. If the tubular is not maintained in the desired centered position, torque monitoring is difficult or impossible.
(2) Multiple link chains employ links which, because of their shape, can slip at high torques.
(3) The high load needed to rotate a tubular to acceptable torque levels can induce undesirable wear on moving parts.
(4) A tong using pivotable arms or gate members to hold a tubular within the tong body can be transformed into a dangerous projectile if the arms' activating or control mechanism fails allowing the tong to disengage from the tubular.
(5) High loads can crush relatively fragile tubulars.
(6) Slippage (which can cause galling and other damage to tubulars) will occur if the gripping element (belt, chain, etc.) loading mechanism cannot maintain an adequate preload force on the tubular.
Relatively Fragile Tubulars and Premium Tubulars
Both the jaw/die tongs and the belt/chain tongs described above can be used with (and are usually used with) relatively hard and rigid metal tubular such as casing and tubing. When such tongs are used with thick tubulars or tubulars made from relatively "softer" metals or from premium metals such as high alloy steels or low carbon steels or tubulars made from non-metal materials such as fiber glass, they often literally chew up the tubular. Manufacturers of such tubular have recommended against the use of any tong with dies or with hard contact means such as chains. On the other hand, the use of strap wrenches was recommended; but available strap wrenches are inadequate because of the inability to precisely control the torque applied with such wrenches--a problem which is compounded by the fatigue of users since the use of such wrenches requires considerable physical labor. Leaking and pollution may occur if a worker thinks a tight makeup has been achieved when in fact optimum torque has not yet been reached.
When working with fiber glass reinforced pipe, serrated or toothed dies (or jaws with such dies) can easily cause marking or damage to tubulars. Such damage results in destruction of reinforcing filaments in the tubular and can considerably reduce the tubular's strength. When the outside surfaces of the fiber glass pipe are irregular or outside diameters of individual joints vary, either inadequate or extreme die penetration is achieved.